The present invention relates generally to corrosion inhibitors, and more particularly to corrosion inhibitors comprising reaction products of a thiol compound and an aldehyde compound and methods of using such inhibitors.
Metals such as carbon steel alloys, copper and its alloys, chrome alloys, and nickel alloys are commonly used in subterranean application equipment (such as in drilling pipes and mixing tanks) and installations (such as gravel pack screens, tubing, and casings). Oftentimes, these metals are subjected to corrosive fluids during subterranean operations.
One such corrosive fluid is an acidizing fluid. Subterranean hydrocarbon-containing formations penetrated by well bores are commonly treated with aqueous acid solutions to stimulate the production of hydrocarbons therefrom. One such treatment known as “acidizing” involves the introduction of an aqueous acid solution into the subterranean formation under pressure so that the acid solution flows through the pore spaces of the formation. The acid solution reacts with acid soluble materials contained in the formation thereby increasing the size of the pore spaces and the permeability of the formation. Another production stimulation treatment known as “fracture-acidizing” involves the formation of one or more fractures in the formation and the introduction of an aqueous acid solution into the fractures to etch the fracture faces whereby flow channels are formed when the fractures close. The aqueous acid solution also enlarges the pore spaces in the fracture faces in the formation. Some commonly used acids include hydrochloric acid, hydrofluoric acid, acetic acid, formic acid, citric acid, ethylene diamine tetra acetic acid (“EDTA”), and combinations thereof.
In carrying out acidizing and fracture-acidizing treatments in wells and other similar treatments using aqueous acid solutions, the corrosion of metal tubular goods, pumps, and other equipment is often a problem. The expense associated with repairing or replacing corrosion damaged metal tubular goods and equipment can be very high. In a well treatment utilizing an aqueous acid solution, the corrosion of metal surfaces in tubular goods and equipment results in at least the partial neutralization of the aqueous acid solution before it reacts with acid-soluble materials in the subterranean formation to be treated. Also, the presence of dissolved metals in the aqueous acid solution can bring about the precipitation of insoluble sludge when the aqueous acid solution contacts crude oil which can in turn severely damage the permeability of the subterranean formation being treated.
Another commonly used corrosive fluid is heavy brine. Heavy brines are often used in the drilling of a well bore into a subterranean formation. It is necessary to cool the drill bit as it cuts into the formation and to remove the drill cuttings from the well bore. Normally, a drilling fluid is circulated downwardly through the drill pipe within the well bore and outwardly through nozzles or openings in the drill bit. The drilling fluid then passes upwardly through the well bore annulus to the surface. Commonly employed drilling fluids are high-density aqueous brine solutions. For example, calcium chloride solutions can be produced having a density up to about 11.7 pounds per gallon of solution. Calcium bromide can be used to produce aqueous brines having a density of up to about 14.2 pounds per gallon. The incorporation of solid calcium chloride pellets in the brine permits a fluid having a density of about 15 pounds per gallon to be formed. When heavy brine solutions having a density greater than 15 pounds per gallon are required, aqueous solutions of zinc halides, such as zinc chloride or zinc bromide, normally are employed, either individually or as blends with calcium halides. Most of the heavy brine solutions are highly corrosive to metals and, therefore, require the addition of expensive inhibitors to the solutions to protect metal surfaces contacted by the fluids.
Many corrosion inhibitors are useful only at selected temperature levels or pH ranges for the various heavy brines and dilution, temperature changes or any change which affects the pH of the brine often results in loss of the corrosion inhibition. Particular problems arise in the selection of corrosion inhibitors for use in zinc halide-containing heavy brine solutions. Many common corrosion inhibitors, such as organic thiophosphates, quaternized amines, polyphosphate esters, filming amines, and the like form precipitates or are ineffective when admixed with zinc halide-containing heavy brine solutions.
A variety of metal corrosion inhibiting formulations for use in aqueous acid solutions have been developed and used successfully heretofore. Many of such corrosion inhibiting formulations have included quaternary ammonium compounds as essential components, particularly in high temperature applications. However, problems have been associated with the use of quaternary ammonium compounds in that they are generally highly toxic to aquatic organisms. Further, the quaternary ammonium compounds that achieve high degrees of metal corrosion protection at high temperatures are those that have relatively high molecular weights and high degrees of aromaticity. Those quaternary ammonium compounds are not readily available commercially and are very expensive to produce.